An industrial effluent contains suspended colloidal particles of clay carrying negative su… — JAMB UTME

An industrial effluent contains suspended colloidal particles of clay carrying negative surface charges, with particle diameters ranging from $1\text{ nm}$ to $100\text{ nm}$ . To treat the effluent, equal volumes of four different $0.01\text{ mol dm}^{-3}$ electrolyte solutions— $Al_2(SO_4)_3$ , $CaCl_2$ , $NaCl$ , and $Na_3PO_4$ —are evaluated for their ability to induce coagulation. Which electrolyte has the highest precipitating power (lowest coagulation value) for this clay colloid, and what is the physical mechanism causing coagulation?

$Al_2(SO_4)_3$ , because the trivalent cation ( $Al^{3+}$ ) carries the highest positive charge to neutralize the negative charges on the colloidal particles, causing them to aggregate into particles larger than $100\text{ nm}$ .Cevap
B
$Na_3PO_4$ , because the trivalent phosphate anion ( $PO_4^{3-}$ ) provides the highest charge density to neutralize the colloidal dispersion.
C
$NaCl$ , because its low formula mass enables rapid diffusion into the colloidal particles, converting the colloid into a true solution of particle size under $1\text{ nm}$ .
D
All four electrolytes possess equal precipitating power because coagulation depends strictly on the total molar concentration of solute particles rather than ionic charge.

Cevap

The electrolyte with the highest precipitating power is

Al_2(SO_4)_3

because the trivalent cation (

Al^{3+}

) effectively neutralizes the negative surface charge on the clay particles according to the Hardy-Schulze rule.

The clay colloidal particles are negatively charged with diameters between

1\text{ nm}

and

100\text{ nm}

. According to the Hardy-Schulze rule, the coagulating power of an electrolyte is determined by the ion bearing a charge opposite to that of the colloidal particles, and it increases rapidly with the valency of the active ion. For a negative sol, cations are active. The trivalent

Al^{3+}

ion from aluminium tetraoxosulfate(VI) has a significantly higher precipitating power than divalent

Ca^{2+}

or monovalent

Na^{+}

, neutralizing the charge and aggregating particles beyond

100\text{ nm}

Adım Adım Çözüm

Identify the charge carried by the colloidal clay particles.

The clay particles are negatively charged lyophobic colloidal particles in the size range

1\text{ nm}

100\text{ nm}

Coagulation requires neutralizing the electrostatic repulsion between colloidal particles using an oppositely charged ion.

Apply the Hardy-Schulze rule to determine which ion causes precipitation.

Positively charged cations (

Al^{3+}

Ca^{2+}

Na^{+}

) are responsible for coagulating the negative colloid.

Ions possessing a charge opposite to that of the colloidal sol are effective for coagulation.

Compare the valencies of the effective cations present in the electrolytes.

Al^{3+}

has a valency of

+3

Ca^{2+}

has

+2

, and

Na^{+}

has

+1

Precipitating power increases exponentially with increasing valency of the active ion (

Al^{3+} > Ca^{2+} > Na^{+}

Relate charge neutralization to particle size change.

Neutralized particles coalesce into larger aggregates (

>100\text{ nm}

) that precipitate out.

Removal of surface charge reduces electrostatic repulsion, allowing van der Waals forces to aggregate colloidal particles into suspension-sized precipitates.

Anahtar Kavram

Hardy-Schulze Rule and Coagulation of Colloidal Systems

Soru

Cevap

Adım Adım Çözüm

Anahtar Kavram

Sık Yapılan Hatalar

Konular